This invention relates to surface coated fillers, especially surface coated inorganic fillers useful in organic moldable resins.
The relative high price and short supply of organic resin feedstocks, especially those useful for producing molded products, have caused many processors to incorporate fillers into the resins before final processing. Since, on a volume basis, fillers are less expensive than organic resins, filled resin products will have a lower raw materials cost than similar unfilled products of the same volume.
As well as lowering cost, fillers will often either increase or decrease certain physical properties. Desirably, a filler will either have no effect on, or will improve each property. While many manufacturers of fillers claim that their products will improve certain properties, these improvements are often minimal or nonexistant. Further, they often also deleteriously affect other properties.
One significant problem encountered when fillers are incorporated into organic resins is that, while the resins are relatively hydrophobic, fillers are typically hydrophilic. This causes processing problems, in that it is difficult for the resin to "wet" the filler. One method used to circumvent this problem is wetting the filler with organic compounds such as mineral oil, calcium stearate, organic titanates, organic silanes, and stearic acid. Another method has been to polymerize a capsule of organic polymer around the filler particles. Each of the these methods, however, suffers from various inherent inefficiencies and side effects such as high energy requirements, high materials cost, and poor filled resin properties.
A more recently developed process has been to coat fillers with organic polymer from a "slurry." This process is described in U.S. patent application Ser. No. 265,761, filed May 21, 1981, now abandoned. While certainly an operable method, even this method suffers from problems. Specifically, when fillers prepared by this method are placed into an organic resin, their physical properties are still not as great as would be desired. Further, this method is inoperable for acidic fillers such as glass beads, silica, and many clays. Further drawbacks of the slurry treatment method include the high cost of drying fillers coated from aqueous slurries and freezing problems in cold climates.
An even more recent advance has been the "dry treatment" taught by U.S. patent application Ser. No. 379,220, filed May 17, 1982. While this method is a marked improvement over the aforementioned "slurry" process, it would still be desirable to have improved physical performance of organic resins filled with coated fillers.